Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $95.64   6.155%   $101.5266   $101.53   $101.55   $101.50  
  Purchase #2 $230.79   8.663%   $250.7833   $250.78   $250.80   $250.80  
  Purchase #3 $240.79   8.371%   $260.9465   $260.95   $260.95   $260.90  
  Purchase #4 $18.69   10.582%   $20.6678   $20.67   $20.65   $20.70  
  Purchase #5 $108.61   4.849%   $113.8765   $113.88   $113.90   $113.90  
  Purchase #6 $222.84   8.578%   $241.9552   $241.96   $241.95   $242.00  
  Purchase #7 $30.55   3.768%   $31.7011   $31.70   $31.70   $31.70  
  7 purchase totals = $947.91       $1,021.4570   $1,021.47   $1,021.50   $1,021.50